8. The Source Catalog

A typical coadded FIRST image covering 0.41 contains pixels, but only discrete radio sources above a threshold of 0.75 mJy. Thus, while the maps are a valuable resource as an archival image of the radio sky, as well as for such tasks as deriving upper limits to sources found at other wavelengths, the most useful scientific product of the survey is the source catalog. Given the highly non-Gaussian characteristics of the noise in snapshot images and the large variety of morphologies exhibited by various radio source populations, automatic extraction of a highly reliable and complete catalog from the FIRST images is a nontrivial task. However, because of its scientific importance for users, as well as the central role it plays in characterizing image quality and integrity, we have expended considerable effort in developing algorithms to produce a source catalog. We expect to continue these efforts for some time to come. Nonetheless, we now have a functioning source extraction program which has generated a preliminary catalog from the 1993 dataset which contains 27,680 entries and can be retrieved via the FIRST home-page where a more detailed description can be found. A paper describing the catalog construction process is in preparation (White et al. 1995).